In spite of the extreme precision of machining operations and their high reproducibility, adjustments must nearly always be made either during an assembly operation or, more frequently, during an adjustment or setting operation, in particular for adjustment of the frequency, adjustment of unbalance or an adjustment of inertia in the case of movable pieces.
It is at the assembled stage in particular that it is necessary to perfect the pairing of certain components, which when taken independently are within machining or production tolerances, but which cannot be assembled purely because of the service stresses specific to the mounted assembly.
This is particularly the case with the regulating organs of timepieces, and more specifically with sprung balance assemblies. In fact, it appears that the unbalance adjustments and inertia adjustments, both static and dynamic, are already very delicate at the individual component stage and that these setting operations turn out to be particularly complex when the components are assembled together. In particular, dynamic adjustments prove to be complicated to implement, in particular frequency adjustment.
The situation is even more complex when such an assembly is already integrated into a larger assembly such as a watch movement, for example, because of the poor accessibility, but also because of the disturbance to proper operation of the movement caused by performing an adjustment, control or balancing operation.
There is therefore a dual difficulty, since it is a matter of being able to manage the dynamic controls and adjustments on components, which are:
moving, or
integrated into a timepiece movement, or
moving and integrated into a timepiece movement.
The problems associated with dynamic balancing are still the domain of an extremely limited number of specialists in industry, which can be verified by the paucity of industrial balancing machines available globally. The field of micromechanics can only magnify this phenomenon, since the pieces to be balanced have a very low mass in the order of one gram or decigram and have inertia tolerances in the microgram×square centimeter range. This has nothing to do with the field of using balancing machines for the wheels of motor vehicles, which are the mot numerous, or machines dedicated to heavy industry, railways or high-speed processing.
The problems associated with dynamic balancing have long been the inspiration for solutions relating to localising zones of the addition or removal of material and to quantifying these additions and removals, which are performed after stoppage of the rotation of the movable element to be balanced, as in the patent document U.S. Pat. No. 2,538,528 in the name of Kohlhagen. In a variant, as in the patent document DE 1 142 796 in the name of Hettich, elements have to be positioned or conversely to be pressed into pre-drilled holes over the entire circumference of a watch balance. Patent CH 367 444 in the name of OMEGA shows the disadvantages of traditional removal by milling on watch balances and proposes a solution of adding or removing material by electrochemical means, as a result of which correction of the mass and the precision of the balancing can be assured.
U.S. Pat. No. 3,225,586 in the name of HAMILTON proposes the use of the microphone of a “Watchmaster” type of machine connected to the rotatable meter to very precisely determine the adjustment of 4 screws on the periphery of the rim of the balance.
To improve these processes in two steps: measurement then adjustment, a patent CH 390 165 in the name of Zenger proposes a process for balancing by electro-erosion continuously with a very slight delay after a stroboscopic measurement, but this requires a rotation in a uniform direction of this balance.
Patent CH 690 874 in the name of Witschi also describes a process for the removal or addition of material following a preliminary measurement with a stop device of the balance to hold it to face removal or adding devices.
Patent CH 526 097 in the name of the Compagnie Générale d'Electricité proposes a balancing of a turning or oscillating piece by beam parallel to the pivot axis of the piece to be balanced comprising an optical device for deviation of the beam such that this is synchronous with the moving piece, and to thus vaporise the material at the appropriate location for the whole duration of the pulse emitted by the laser. This technology represents significant progress in relation to the prior art, but is not well suited to a component mounted in an assembly because of the waste material and contamination of the assembly.
The same applies for patent FR 2 159 367 in the name of Les Fabriques d'Assortiments Réunies, which proposes a machining process with minimisation of the number of operations, but wherein the position of the machining head depends on the fault to be corrected, which is not possible in a mounted assembly.
Overall, the known processes capable of conducting a correction of inertia or balancing or other physical magnitude such as the rigidity of a spring on a moving piece are rare and ill-suited to conducting this correction on this same piece mounted in an assembly. Moreover, they are little suited to an alternating movement, which applies to a balance or a mounted sprung balance assembly.
U.S. Pat. No. 6,534,742 in the name of ETA SA Fabrique d'Ebauches proposes a method for adjusting the oscillation frequency of a spring balance by using a laser acting on the spiral spring to reduce its elastic torque by reducing it thickness or its height. While it represents obvious progress in relation to the prior art, this instruction does not resolve all the cases in question, since it can only create loss by weakening the spring. On the other hand, it can only be used outside the timepiece movement because of the contamination and waste materials generated by the action of the laser.